Cast iron component for enveloped casting, enveloped casting product using it, and method for producing cast iron component for enveloped casting
1. Field of the Invention
The present invention relates to a cast iron component for enveloped casting suitable for, for example, a cylinder liner or an insert for a brake drum; an enveloped casting product using it, and method for producing the cast iron component for enveloped casting.
2. Background of the Invention
In aluminum cylinder blocks for engines of automobiles (hereinafter referred to as cylinder block), cylinder liners (hereinafter sometimes referred to as liner) made of cast iron are often used in order to satisfy desired seizing resistance and wear resistance of a sliding surface. As a method for producing the cylinder block having the liner enveloped or embedded therein, a method for enveloped casting has been known wherein a liner is placed within a cast mold for the cylinder block and the periphery of the liner is enveloped with aluminum or an aluminum alloy (hereinafter referred to as an aluminum material).
In such a liner, it is required to secure adhesion between the outer face of the liner and the aluminum material to prevent the liner from rotating at the time of processing the inner face of the liner after the enveloped casting or to improve the engine performance by the reduction in the deformation of bores and the improvement of thermal conductivity. The following methods have been known to obtain a liner having a high adhesion with the aluminum material.
(1) a method wherein shot peening is applied to the outer face of the liner to provide irregularities on the outer face, thereby improving the adhesion (JP-B-2-29426).
(2) a method wherein spinies (acicular special cast surface) are formed on the outer face of the liner to improve the adhesion (JP-B-43-4842).
(3) a method wherein grooves in an axial direction are formed by machining the outer face of the liner to improve the casting properties of the block and the adhesion (JP-A-8-290255).
(4) a method wherein blast finishing is applied to the cast iron surface of the outer face of the liner. It has been known that the cast iron surface in this case is obtainable by a permanent mold centrifugal casting method or the like wherein a suspension containing from 20 to 40 mass % of diatomaceous earth having a mean particle size of not more than 0.1 mm, from 2 to 10 mass % of bentonite and from 65 to 80 mass % of water, is coated by spraying on the cast mold, and after drying it, a melt of cast iron is poured thereinto.
FIG. 1 shows an example of a cylinder block having a liner enveloped, which is produced by enveloping the liner. in this figure, 1 is a cylinder block having a liner enveloped, 2 is a liner, 3 is an aluminum material and 4 is the shortest interval between bores. Between the bores, as a wall, there are two liner 2 parts and an aluminum material 3 part sandwiched by them as illustrated in this figure. Conventionally, the shortest interval 4 between the bores has been set to be at least 9 mm. However, it has been recently demanded to set the shortest interval to be at most 8 mm, reflecting the tendency toward narrow inter-bore distance to satisfy the desired bore up or weight reduction.
For example, when an aluminum cylinder block having a liner enveloped as shown in FIG. 1 is made by die-casting, usually, the thinnest aluminum part between the bores solidifies at first, and then peripheral portions solidify. However, when the distance between the bores is narrowed, if the adhesion (anchor effect) between the liners and the aluminum material between the bores is insufficient, the thinnest aluminum material part is pulled at the time of shrinkage by solidification of its peripheral portions, whereby hot crack or hot tearing may sometimes be caused. Further, since the part between the bores solidifies at first, the aluminum material is hardly filled into dents on the outer face of the liner. Accordingly, as the liner for enveloped casting which satisfies the narrow inter-bore distance, it is demanded that the adhesion between the liner and the aluminum material is good, the filling property of the aluminum material into dents on the outer face of the liner is good even between the bores, and the thickness of the liner is thin.
However, the above methods (1) to (4) have the following drawbacks. For example, with the shot peening in the above method (1), the adhesion is insufficient, and further, since a soft ferrite structure is required to exist in a thickness of at least 2.0 mm, the thickness tends to increase. The spinies in the above method (2), although the adhesion is good, the irregularities on the outer face is at a level of about 1.0 mm and the thickness increases, and further, the filling property of the aluminum material into the dents of spinies is poor. In the machining of grooves in the above method (3), the thickness tends to increase entirely in order to secure the strength at the bottom of groove, and the cost tends to be high. The one in the above method (4) obtainable by blasting the cast iron surface has drawbacks, e.g. poor adhesion, although the filling property of the aluminum material is good and the price is low.
Accordingly, it is an object of the present invention to provide a cast iron component for enveloped casting which is excellent in the filling property of the aluminum material and the adhesion with the aluminum material at the time of die-casting; an enveloped casting product using it, and a method for producing the cast iron component for enveloped casting.
In order to accomplish the above objects, the present invention provides a cast iron component for enveloped casting (hereinafter referred to simply as xe2x80x9ccast iron componentxe2x80x9d) which is characterized by that the cast iron component has a surface to which enveloped casting is applied and which has a surface roughness such that a maximum height Ry is from 65 to 260 xcexcm and a mean spacing of profile irregularities Sm is from 0.6 to 1.5 mm.
The cast iron component of the present invention preferably has the maximum height Ry within a range of from 75 to 250 xcexcm and the mean spacing of profile irregularities Sm within a range of from 0.7 to 1.4 mm. More preferably, the surface to which enveloped casting is applied is a cast iron surface. Moreover, the cast iron component of the present invention is suitable for a cylinder liner or an insert for a brake drum.
The enveloped casting product of the present invention comprises the above cast iron component and aluminum or an aluminum alloy enveloping the cast iron component.
The enveloped casting product of the present invention is particularly suitable for a cylinder block or a brake drum. Further, when the enveloped casting product is a cylinder block, the cylinder block preferably has a shortest interval between bores of from 5.0 to 8.0 mm at the time of completion of the cylinder block.
Furthermore, the method for producing a cast iron component for enveloped casting of the present invention is a method for producing a cast iron component which has a surface to which enveloped casting is applied and which has a surface roughness such that a maximum height Ry is from 65 to 260 xcexcm and a mean spacing of profile irregularities Sm is from 0.6 to 1.5 mm, by coating a facing on a heated inner face of a cast mold, drying it, and pouring a melt of cast iron into the cast mold for molding, wherein the facing is a suspension comprising from 20 to 45 mass % of silica sand having a mean particle size of from 0.05 to 0.5 mm, from 10 to 30 mass % of silica flour having a mean particle size of not more than 0.1 mm, from 2 to 10 mass % of a binder and from 30 to 60 mass % of water.
In the method of the present invention, preferably, the coating of the facing and the pouring of the melt of cast iron are carried out while rotating the cast mold.
According to the present invention, the cast iron component has a surface to which enveloped casting is applied and which has a surface roughness such that a maximum height Ry is from 65 to 260 xcexcm and a mean spacing of profile irregularities Sm is from 0.6 to 1.5 mm, and when, for example, an aluminum material is die-cast on the outer face of the cast iron component, the filling property of the aluminum material into the irregularities is excellent, and an enveloped casting product excellent in the adhesion with the aluminum material can be obtained. Accordingly, when the present invention is applied to, for example, a cylinder liner, the liner and the aluminum material are fixedly adhered and it is thereby possible to prevent hot cracks or the like of the aluminum material in narrow distance between bores.
Further, according to the method of the present invention for producing the cast iron component for enveloped casting, by using, as a facing, a suspension comprising from 20 to 45 mass % of silica sand having a mean particle size of from 0.05 to 0.5 mm, from 10 to 30 mass % of silica flour having a mean particle size of not more than 0.1 mm, from 2 to 10 mass % of a binder and from 30 to 60 mass % of water, it is possible to easily obtain a cast iron surface which has a surface roughness such that a maximum height Ry is from 65 to 260 xcexcm and a mean spacing of profile irregularities Sm is from 0.6 to 1.5 mm. Accordingly, by using this cast iron surface as a surface to which enveloped casting is applied, it is possible to obtain an enveloped casting product excellent in the adhesion between the cast iron component and the surrounding aluminum material on its periphery as mentioned above.